OBJECTIVE: To investigate whether Treg cells can suppress osteoclast differentiation, and to define a new potential link between the immune system and the skeleton.
METHODS: Regulatory CD4+,CD25+,Foxp3+ T cells were isolated and purified from the spleen and cocultured with CD11b+ osteoclast precursor cells isolated from bone marrow. Osteoclastogenesis and bone erosion were assessed by tartrate-resistant acid phosphatase staining and pit resorption assay, respectively. In addition, Transwell experiments and cytokine-blocking experiments were performed to define the mechanisms of interaction between Treg cells and osteoclasts.
RESULTS: CD4+,CD25+,Foxp3+ T cells, but not CD4+,CD25- T cells, dose dependently inhibited macrophage colony-stimulating factor- and RANKL-dependent osteoclast formation. Pit formation was inhibited by up to 80% when Treg cells were added. The blockade of osteoclast formation was not based on the alteration of RANKL/osteoprotegerin balance but was essentially dependent on direct cell-cell contact via CTLA-4. Treg cell-mediated expression of transforming growth factor beta, interleukin-4 (IL-4), and IL-10 contributed but was not essential to the inhibitory effect on osteoclastogenesis.
CONCLUSION: These data show that CD4+,CD25+,Foxp3+ Treg cells suppress osteoclast formation, provide a new link between the immune system and bone, and extend our knowledge on regulation of bone homeostasis by the immune system.
- Antigens, CD/pharmacology
- Antigens, Differentiation/pharmacology
- Bone and Bones/cytology
- CD11 Antigens/metabolism
- CTLA-4 Antigen
- Cell Communication/physiology
- Cell Differentiation/drug effects
- Cells, Cultured
- Forkhead Transcription Factors/metabolism
- Immune System/physiology
- Interleukin-2 Receptor alpha Subunit/metabolism
- Macrophage Colony-Stimulating Factor/pharmacology
- Mice, Inbred C57BL
- RANK Ligand/physiology
- T-Lymphocytes, Regulatory/cytology